Agile beam laser

Abstract

A laser system for providing a rapidly steerable laser output beam. The laser system includes a phase conjugate reflector, laser gain medium and its associated pump source, an output coupling device, and an optical element which selectably controls the transverse lasing mode of the laser system. The components are arranged to form a laser oscillator between the phase conjugate reflector and the optical device, and is operated in such a manner that each selected transverse mode of laser operation generates an output beam from the system which has a different wavefront tilt. Accordingly, the output beam is steerable and is dependent upon the selected transverse mode which is currently lasing in the oscillator.

What is claimed is: 
     
       1. Laser apparatus comprising: phase conjugate reflecting means for reflecting laser energy which is the phase conjugate of laser energy incident thereupon;   optical means for providing a plurality of selectable transverse lasing modes between said optical means and said phase conjugate reflecting means, each of said plurality of transverse lasing modes having a predetermined wavefront tilt in the near field;   laser gain medium disposed between said optical means and said phase conjugate reflecting means for providing said laser energy which is reflected therebetween;   laser pumping means operatively connected to said laser gain medium for providing excitation energy for said laser medium; and   output coupling means disposed adjacent to said optical means in said near field for coupling a portion of said laser energy out of said laser apparatus as an output beam therefrom;   whereby said output beam is steerable in position determined by the particular transverse lasing mode selected by said optical means.   
     
     
       2. The laser apparatus of claim 1 wherein said optical means comprises: a lens; and   an electronically controllable reflective element disposed at the focal plane of said lens, said mirror element having a reflective surface whose transverse location in said focal plane is selectively controlled to produce said plurality of transverse lasing modes.   
     
     
       3. The laser apparatus of claim 1 wherein said optical means comprises: first and second lenses;   an electronically controllable spatial filter disposed between said first and second lenses at respective focal planes thereof, said spatial filter having a transmissive portion whose transverse locations is selectively controlled to produce said plurality of lasing modes; and   a reflecting element disposed adjacent to said second lens for reflecting light transmitted by said spatial filter back through said spatial filter.   
     
     
       4. The laser apparatus of claim 2 wherein said electronically controllable reflective element further comprises: a slab of electro-optical material;   a first layer of electrodes in the form of parallel strips disposed on a first face of said slab being substantially transparent for said laser energy;   a second layer of electrodes in the form of parallel strips disposed on a second face of said slab which is on the opposite side of said slab from said first face, with the length of said second electrode strips positioned perpendicular to the direction of the length of said first electrode strips, and being substantially 100% reflective for said laser energy; and   electrical input means connected to both layers of said strip electrodes for supplying a control voltage to at least one electrode in said first layer and at least one electrode in said second layer for creating at least one localized volume of predetermined polarization within said slab whose dimensions are on the order of a diffraction limited beam, whereby incident radiation is transmitted through said slab to said reflective second electrodes and reflected at an angle dependent upon the planar position of said localized volume of polarization.   
     
     
       5. The laser apparatus of claim 4 wherein said slab of electro-optical material comprises potassium dihydrogen phosphate. 
     
     
       6. The laser apparatus of claim 4 wherein said first electrodes comprise indium tin oxide. 
     
     
       7. The laser apparatus of claim 4 wherein said second electrodes comprise silver. 
     
     
       8. The laser apparatus of claim 2 wherein said electronically controllable reflective element further comprises: a slab of photo-refractive material;   optically reflective means adjacent to a first side of said slab;   a quartz plate positioned adjacent to a second side of said slab which is on the opposite side of said slab from said reflective means;   polarization means positioned adjacent to said quartz plate on the side of said plate opposite said slab;   an electron beam whose output energy is sufficient to alter the birefringence of the photo-refractive material in said slab over a predetermined volume; and   control means for directing said electron beam output energy to positions in said slab such that the birefringence of said slab material is altered so as to compensate for the birefringence of said quartz plate and allow laser energy from said polarization means to be transmitted through said slab and reflected by said reflective means.   
     
     
       9. The laser apparatus of claim 8 wherein said reflective means comprises a plane mirror. 
     
     
       10. The laser apparatus of claim 8 wherein said reflective means comprises a reflective coating of metallic material deposited on said first side of said slab. 
     
     
       11. The laser apparatus of claim 2 wherein said electronically controllable reflective element further comprises: a planar mirror substrate coated with a layer of vanadium dioxide;   means for heating said mirror substrate to an elevated temperature close to but just below the predetermined semiconductor-metal transition temperature for said vanadium dioxide; and   an electron beam whose output beam is programmably directable over the surface of said mirror substrate and has sufficient energy to raise the temperature of said vanadium dioxide in at least one localized area, whose dimensions are on the order of the cross section of a diffraction limited beam for said laser, above the transition temperature whereby a reflective metal exists within said localized area.   
     
     
       12. The laser apparatus of claim 3 wherein said electronically controllable spatial filter further comprises: a slab of electro-optical material;   a first layer of electrodes in the form of parallel strips disposed on a first face of said slab being substantially transparent for said laser energy;   a second layer of electrodes in the form of parallel strips disposed on a second face of said slab which are on the opposite side of said slab from said first face, with the length of said second electrode strips positioned perpendicular to the direction of said first electrode strips, and being substantially transparent for said laser energy; and   electrical input means connected to both layers of said strip electrodes for supplying a control voltage to at least one electrode in said first layer and at least one electrode in said second layer for creating at least one localized volume of predetermined polarization within said slab whose dimensions are on the order of a diffraction limited beam, whereby incident radiation is transmitted through said slab and electrodes at a position dependent upon the planar position of said localized volume of polarization.   
     
     
       13. The laser apparatus of claim 12 wherein said slab of electro-optical material comprises potassium dihydrogen phosphate. 
     
     
       14. The laser apparatus of claim 4 wherein said first and second electrodes comprise indium tin oxide.